Of UnderWater Quests and Useless 'Inators'
by Sally the Sunflower
Summary: Phineas, Ferb and Co build a submarine and set off in search of adventure. However, when they crashland in Bikini Bottem it is up to Sponge-Bob and his friends to help the children in their search for the parts they need to get home.


_Disclaimer: I don't own any of the characters mentioned in this story. I can't afford the rights._**  
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**Chapter One: Of boredom and marine biology documentaries.**

As usual Phineas and Ferb began their day balmed out under the big tree in their back garden. Perry, their pet platypus, sat between them. It was a warm day with the odd gentle, cool breeze and the nice conditions were making the thought processes of the step-brothers sluggish.

"Ferb," said Phineas breaking the silence, "I have absolutely no idea what we're gonna do today." The holidays were drawing to a close and, as far as Phineas was concerned at the moment, they had done everything possible. Plus a few things that weren't. Ferb looked thoughtful for a moment before shrugging. "We…could…build a rollercoaster?" suggested Phineas sitting up. As an answer Ferb pulled a photograph out of his pocket. It was of them, their friends and the rollercoaster they had built earlier in the summer. "Oh ya," said Phineas, lying back down. "Hmm…how about a beach?" Ferb just responded in the same way. "Monster truck rally? Rocket? Super heroes? Time travel?" Phineas suggested many more activities for the day but Ferb kept foiling his plans with a photo pulled from his back pocket. "Where do you even keep all of those?" asked Phineas raising an eyebrow. Ferb just shrugged.

At this point the boys were interrupted by Isabella's head appearing over the garden fence.

"What'cha doin'?" she sang.

"Oh, hey Isabella. Ferb and I were just trying to figure out what to do today. Got any ideas?"

"Don't look at me. I usually leave that up to you two," she replied beaming. Right, thought Phineas, that's helpful. Sighing he got up.

"C'mon, let's go see what Baljeet's up to." The other two followed him out of the garden.

* * *

><p>The humans were gone. Now was his chance. Perry the platypus stood upright, pulled his brown fedora out of somewhere and put it on his head. He loved his brown fedora, fedoras were cool.<p>

Suddenly the ground went from beneath his feet and he was falling. He really did hate all these secret entrances. Would it kill them to use the one? Also, was he the only one who thought the way new ones kept being installed around the house without anyone noticing was creepy?

Perry's inner complaints were interrupted by a face-full of tiles.

"Oooo. Sorry about that agent P. We've changed secret entrance installers. Those other guys were charging crazy prices. Their excuse was something about quality and safety. Anyway, we went with this cheaper company. In hindsight we probably should have listened."

Perry picked himself up off the floor and waddled over to his chair in front of the oversized screen. There were times when he really didn't like this man. This was one of them.

"But that doesn't matter right now there are more serious issues are at hand. Doofenschmirtz is up to his usual shenanigans," said Monogram, his face and voice becoming grave. Ooo, thought Perry, another defective 'inator'. They really did give that guy too much credit. Even if he wasn't there to foil him he'd probably end up foiling himself. Then again, at least he made Perry's job easy. "Intelligence reports tell us he has purchased a tiny, deserted, tropical island in the middle of no-where. This can only mean he is up to one of his evil schemes." Sure, thought Perry, the guy who can't cause trouble in the middle of a busy city is bound to raise all kinds of hell in the uninhabited middle of no-where. "I'm sending you the co-ordinates now." Nothing happened. " Emm… just a moment agent P," Monogram turned from the screen, " Carl! Where are the co-ordinates? I told you to have them ready!"

"Sorry sir," a flustered looking Carl appeared on screen, "Here they are sir," he handed Monogram a slip of paper.

"Thank you Carl."

"Yes sir." Carl remained where he was as an awkward silence fell on the trio.

"You can go now Carl."

"Right sir, yes sir." Carl disappeared off screen and Monogram turned back to Perry.

"Sorry about that agent P. Now where was I? Oh yes, I'm sending you the co-ordinates now." A piece of paper appeared out of a slot near Perry. He took a quick look at it before carefully putting it away somewhere. Presumably the same place he keeps his fedora. Wherever that is.

"Good luck Agent P!" Monogram called out after him as he raced out of the room.

* * *

><p>Ferb rang the door bell and the trio waited in silence. Once again it was Phineas who broke it.<p>

"Hey, where's Perry?" The three looked around before concluding that once again Perry had disappeared. "I'd love to know where it is he goes," mused Phineas.

It was then that Baljeet opened the door and raced away again quickly, shouting "Come on in!" as he went. The three friends stood confused in the doorway for several moments.

"I suppose we better go in," suggested Phineas.

The children found their friend sitting in the front room watching the telly.

"What'cha watchin'?" asked Isabella as the three plonked down on various seats.

"Only the most amazing marine biology documentary ever!" he exclaimed. The children watched as a diver swam around a choral reef filled with bizarre looking fish, some of which didn't even look like fish. "Isn't it amazing?" Baljeet was practically bouncing in his seat with excitement.

"It looks….. interesting," Isabella ventured, tilting her head to the side and scrunching up he eyes in an effort to make sense of the creature on the screen which apparently claimed itself to be a fish.

Suddenly, Phineas leapt out of his seat, one finger pointing triumphantly in the air.

"I know what we're going to do today!" The others all leapt too at the suddenness of his movement. "We're going to build a submarine. Then we can go exploring like they guy on T.V." Ferb reached for his back pocket and Phineas grabbed his wrist. "Don't even think about it." Then he ran from the room dragging a helpless Ferb behind him. Isabella skipped out after the two. Baljeet hesitated a moment considering weather this might be worth missing the most amazing marine biology documentary ever.

"It better be," he muttered to himself and followed the others out the door.

**A/N: So, that was chapter one, hope you enjoyed. I decided to write this when a cousin of mine mentioned that he loved the idea of these two fandoms coming together. I hope I didn't disapoint you 'cuz. Anyway, please review. All constructive critacisim is welcome.**


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